They are microscopic organisms that hunt down and kill grubs of all kinds. You apply them by putting them in water and then spraying them on the lawn, then water them in. They live (and reproduce) as long as they can stay wet in the soil. They will wipe out a lawn grub infestation.

Note that there are also nematodes that are herbivores. They are bad news if you get them in your soil, because they eat the roots of your plants. These are very different--they only eat larva, not plants.

If these lawn care guys don't get a handle on your grub problem, you ought to try nematodes. They work very well.